ABS Description. Chevrolet PJJ 2000

For 1990-2009 cars

The Antilock Braking System consists of the following components:

• | A conventional hydraulic brake system

• | Antilock components

The conventional brake system includes the following components:

• | A vacuum power booster

• | A master cylinder

• | Front disc brakes

• | Rear drum brakes

• | Interconnecting hydraulic brake pipes

• | A low fluid sensor

• | A red BRAKE warning indicator

The ABS includes the following components:

• | A Brake Pressure Modulator Valve (BPMV)

• | An Electronic Brake Control Module (EBCM)

• | Four wheel speed sensors

• | The interconnecting wiring

• | An amber ABS warning indicator

### EBCM/BPMV Assembly

#### Legend

1. Electronic Brake Control Module (EBCM)
2. Brake Pressure Modulator Valve (BPMV)

### Brake Pressure Modulator Valve (BPMV)

The Brake Pressure Modulator Valve (BPMV), mounted on the left side of the engine compartment, provides brake fluid modulation for each of the individual wheel circuits as required during Antilock braking. During the Antilock mode, the BPMV can maintain or reduce brake fluid pressure independent of the pressure generated in the master cylinder. The BPMV does not provide more pressure than is applied by the master cylinder during braking.

With the exception of the EBCM, the Brake Pressure Modulator Valve (BPMV) is an integral, non-serviceable component. The BPMV should never be disassembled.

The BPMV consists of several other components which are described as follows:

#### Pump Motor

The BPMV contains a motor driven recirculation pump. The pump reduces pressure during ABS events. It transfers fluid from the brake calipers back to the master cylinder circuit. The pump and motor are located within the BPMV and are not serviced separately.

#### ABS Valves

The ABS valves decrease or maintain brake fluid pressure at the individual wheel circuits. There are four Inlet, and four Outlet solenoid valves. The solenoid valves maintain, increase, or decrease brake fluid pressure to the individual wheel circuits. The EBCM commands the valves to their correct position during an antilock event. During antilock mode, the pressure in each hydraulic circuit can be held or released by activating the appropriate valves. The normal state of the inlet valves is open, while the normal state of the Outlet valves is closed. This allows direct master cylinder pressure to the brakes during normal braking. The ABS valves are located within the BPMV and are not serviced separately.

### Electronic Brake Control Module (EBCM)

The Electronic Brake Control Module (EBCM) is a microprocessor that controls the ABS.

The inputs to the EBCM include the following components:

• | The wheel speed sensors

• | The ignition switch

• | The unswitched battery voltage

The outputs include the following components:

• | Solenoid valves

• | Warning indicators

A serial data line is provided for service diagnostic tools and assembly plant testing.

The EBCM monitors the speed of each wheel and controls the solenoids and pump motor in order to reduce brake pressure to a particular wheel when the wheel is approaching slip.

This cycle will repeat until one of the following conditions exists:

• | The vehicle comes to a stop.

• | The brake releases.

• | The wheel no longer approaches slip.

If any system malfunction is detected, the EBCM will store a Diagnostic Trouble Code (DTC) in nonvolatile memory (DTCs will not disappear if the battery is disconnected).

The EBCM is bolted directly to the BPMV located in the engine compartment.

### Vent Tube

Terminal C11 of the EBCM harness connector is a vent tube that vents the cavity between the EBCM and the BPMV to the atmosphere.

### Front Wheel Speed Sensors and Rings

The front wheel speed sensors are of a variable reluctance type. Each sensor is attached to the knuckle assembly in close proximity to a toothed ring. An AC voltage is generated when the toothed ring passes by the sensor. The magnitude and frequency are proportional to the speed of the wheel and both will increase with increasing speed. The sensor is not repairable, nor is the air gap adjustable.

### Rear Wheel Speed Sensors

The rear wheel speed sensors are mounted in the bearing assembly and are non-adjustable. Sensor gap is set at the time of assembly. This integral hub/bearing/wheel speed sensor assembly is serviced as a complete assembly only.

### EBCM Relay

The EBCM relay is a normally-open contact type.

The EBCM relay has special contact material to handle the high currents required for ABS operation. The relay allows battery voltage and current to be supplied to the solenoids and the pump motor.

The relay is an integral part of the EBCM and cannot be serviced separately.

### Wiring Harness

The wiring harness is the mechanism which electrically connects the EBCM to the following components:

• | The power and the ground

• | The wheel speed sensors

• | The fuses

• | The switches

• | The indicators

• | The serial communications port

The wiring harness consists of the following components:

• | The wires that provide electrical interconnection.

• | The connectors/terminals that provide an electrical/mechanical interface from each wire to a system component.

### Warning Indicators

The Electronic Brake Control Module (EBCM) continuously monitors itself and other ABS components.

If the EBCM detects a problem with the system, the amber ABS warning indicator will light continuously (solid indicator) in order to alert the driver of the problem.

Normal (non-antilock) braking will remain. In order to regain ABS braking ability, the ABS must be serviced.

The amber ABS warning indicator will illuminate any time when the EBCM suspects that the ABS operation is degraded because of a system malfunction.

The red BRAKE warning indicator illuminates when the following conditions exist:

• | The fluid level in the master cylinder is low

• | The parking brake switch is closed

• | The ignition switch is in START

• | Certain ABS DTCs are set

| (This is controlled by the EBCM.)

The red BRAKE warning indicator alerts the driver that a base brake problem may exist.

Refer to Brake Warning Indicator System Check in Hydraulic Brakes for further diagnosis of the red BRAKE warning indicator.

### Fuses

The power distribution system of the vehicle consists of the fuses and the ignition switch.

The system fuses are:

• | The ABS (50A) Fuse

• | The ABS (10A) Fuse